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Need help Minting my Own Gold

Noxx

Plastic
Joined
Oct 10, 2008
Location
Canada, Quebec City
Hello fellow Machinists,
My name is John-Nicholas, and I'm studying in Chemical Engineering.
I need your help because my knowledge in mechanics is limited...

I am currently trying to find a formula to calculate the Force needed to press a 10 grams gold bar. I tried with the Young's Modulus formula, but it does not seem to apply to this case, since I ended up with 1 000 000 kg required... lol

So, does anyone has an idea of the appropriate formula ? I looked in the Machinery's handbook without success. I have the Young's modulus, Poisson's ratio, Yield Strength and Ult Tensile Strength values for gold.

Second question, I would like to know what is the best type of steel to use for this application ? A friend of mine told me to use O type steel. The steel must not deform to high pressure but will not have to handle shocks.

Thank You very much in advance.
 
Thanks for the replies,

stannp368,
My bars will be in rectangular shape.

My current bars (which I poured) are 0.6'' x 0.3'' x 0.15''
They will be cold pressed to 0.7761'' x 0.5174'' x 0.07874''
Or if you prefer: 19.7130mm x 13.1420mm x 2.0mm

surplusjohn,
Thank, I'll take a look.


Thanks guys.
 
There was a thread here on PM a year or two back about coining (actually making coins). The man was planning to use a board-type drop hammer, as I recall. I will let you do the search.

Meanwhile, here is information about a private mint, their products, and their equipment.
http://www.shirepost.com/Coinage.html

As they said, a six pound hammer will get you started, unless you want to compete with Credit Suisse for quality of product.

Larry
 
L Vanice, thanks for the input.

But yes I want to compete with Credit Suisse and such. ;)

To give you an idea, a friend of mine is currently drawing me some plans that will be loaded in a CNC Mill. I want my ingots to be as professional as possible.

Thanks
 
My recollection of a Credit Suisse ingot is that it was probably blanked from rolled sheet and coined between highly polished dies. The average CNC mill would not get the finish on the die sinking of the letters fine enough. Fine abrasive blasting of the die after milling and heat treating will take out the machining marks and leave a frosted finish. Then the flat of the die can easily be mirror polished, producing a frosted raised lettering on a polished background.

I don't know about the tonnage needed, but the good news is that .999 Au is almost as soft as lead, so it will be easier than coining silver or bronze.

This company has knowledge of production jewelry-making and sells used equipment. Perhaps it would pay to call them.
http://goldmachinery.com/information/index.htm

Larry
 
Larry, Thanks again.

You are right, dies are made from highly polished steel. I saw a few vids.

The CNC would do the raw job (lettering, logo and such) then I would hand polish the dies.

Do you think a CNC Mill has the accuracy to make lettering ? The lettering may be only 0.02'' high.

Thanks for the link.
 
Larry, Thanks again.

You are right, dies are made from highly polished steel. I saw a few vids.

The CNC would do the raw job (lettering, logo and such) then I would hand polish the dies.

Do you think a CNC Mill has the accuracy to make lettering ? The lettering may be only 0.02'' high.

Thanks for the link.

It will do, however , to do the fine detail in the steel will take some pretty good small endmills, and run them at the correct surface speed
Think 20 000 rpm + for a .5 mm dia endmill......

Boris
 
The closest U.S. Mint to you would be the one in Philadelphia, PA. It is a very interesting FREE tour and they encourage questions on their operation. I am sure they would be able to get you the answers you need to your technical questions. They would probably even respond to a letterhead request if you can't travel there, but I recommend the tour. There is a very popular exhibit that shows how the dies are made, and one of the visuals is the use of the pantograph to create the stamping dies from a model that is at least 20 times larger than the actual coin to be stamped.

:cheers:
 
that type of die was sometimes made by hobbing. a master was made in steel, then hardened then that was pushed into an annealed steel blank with a big press over several hours, then hardened. this allows mulitiples to be made.
I just looked in my Bliss Power Press Handbook and there is a chart of tonnage for stamping US coins
Double eagle, gold 155 tons
Eagle, gold 110 tons
Half Eagle, gold, 60 tons
Quarter Eagle, gold, 35 tons
Standard dollarm silver, 160 tons
half dollar, silver, 98 tons
quarter dollar, silver, 60 tons
dime, silver 35 tons
nickel, nickel, 60 tons
penny, copper, 40 tons

this was from the 1950 edition but the book was originally written in 20s. This is an excellent book, and I have an extra one that I would sell. send me a pm if interested.
 
You probbably can do it on this machine
It is a reduction machine
As far as I know on the big disk is a template mounted and on the smaller left one the die is mounted Then it is copied and engraved sort of
It is for sale but shipping will set you back a grand at least

Peter
Reducingmach.Jan-Vier3.3.JPG
 
As I remember re: hobbing dies, the steel used was P-20, which is a modified 4135. It was purchased annealed, hobbed on a Hobbing Press (which is what those tonnage figures are about, then heat treated, usually in a reducing atmosphere, then the die comes back to the diemaker for final polishing and detailing.
Hobbing presses are specialized, usually hydraulic, and very robust.
This was a pretty standard way of sinking details in plastic injection molds before EDMs came along. If you have anything over 40 years old with some fine details in it, take a close look. It was probably either hobbed or engraved. In many cases the hob was engraved then sunk into multiple cavities.
I haven't done any hobbing in 35+ years, recently tried to explain it to some younger moldmakers. Nobody believed such a thing was possible. "...But...but, where will the metal go?"
 
As far as I can see there was a big original of the coin made 8 to 10 times as big
That was placed on a machine like on the pic
That machine makes the hob with a possitive image in a 1to1 ratio
That hob is used on a hobbing press to make several dies with a mirrow image
Then on a coinpress the coins are made

Peter
 
I haven't done any hobbing in 35+ years, recently tried to explain it to some younger moldmakers. Nobody believed such a thing was possible. "...But...but, where will the metal go?"

So where DOES the metal go? I assume upwards and outwards, but not evenly. Do you finish the exterior to size after hobbing?
 
re: you can do it with this machine

Hi, I have one of those too. It is called a janvier Lathe. The one I have is German, it too is for sale. If anyone needs it is in Canada and the asking price is $3500 obo. Good luck,Jason
 








 
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